MAINTAINERS: update HSI entry
MAINTAINERS: update HSI entry

Add git tree for hsi subsystem, update Sebastian Reichel's e-mail
address and add Documentation/hsi.txt as maintained file.

Signed-off-by: Sebastian Reichel <1ea78bda3cb6d36efdb8fc89aad6555e21b4887e@kernel.org>
Reviewed-by: Pavel Machek <2375fa63e2908bb2df59f606483a3aa92321db7a@ucw.cz>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs